Recorded discs or records are generally flat circular plates of a plastic material having a center hole therethrough and having recorded information provided on one or both major surfaces of the disc in the form of surface relief patterns. The surface relief patterns are preferably formed in a spiral groove in the major surfaces of the disc, and the center portions and edge portions of the major surfaces of the disc are generally left blank.
Recently there has been developed a high density information recorded disc, such as a video disc, in which there is a very high packing density of the grooves containing the surface relief pattern, on the order of about 10,000 grooves per inch (4,000 grooves per centimeter). To achieve such a high packing density, the grooves must be very narrow, on the order of about 2.7 microns in width, and very shallow, on the order of about 4,000 angstroms in depth. The disc is played with a stylus having a very fine tip which rides in the groove containing the surface relief pattern; and during play of the record, the same is rotated at a relatively high speed, on the order of about 450 r.p.m. Due to the fineness of the grooves and the fine dimensions of the surface relief pattern, any defects or scratches on the surface of the disc can severely disrupt the information in a large number of the grooves and adversely affect the operation of the disc.
A molding apparatus or mold press for molding these high density information recorded discs, such as a video disc, generally includes a pair of opposed mold plates or members, at least one of which is movable toward and away from the other, and which when together form a mold cavity therebetween of the size and shape of the disc to be formed. Secured on the opposed surface of each mold plate is a separate stamper of a thin metal sheet which has on its surface the negative of the surface relief pattern to be formed in the surface of the disc. The stampers generally have an opening in the center thereof and are secured to their respective mold plates by a clamping ring around the outer edge of the stamper and a center hold-down plate extending through the opening in the stamper and engaging the stamper at the edge of the center opening. The center hold-down plates are secured in openings in the mold plates.
One type of these high density information discs is made from a resinous plastic material which is filled with conductive particles, such as carbon black particles, so that the disc is thereby made conductive. However, this type of disc is much more brittle and abrasive than discs which do not contain the conductive particles.
Due to the fine dimensions of the grooves and the surface relief patterns in the grooves, as well as the special materials used in the fabrication of these discs, many of the requirements involved in the molding of and the processes for the replication of these high density information discs are different from those previously used to make audio records. An example of this is that caution must be exercised in the preparation for use and use of the molds or mold members employed in the molding of these high density information discs. If caution is not followed, the mold members may damage the stampers secured thereto, which, in turn, will result in defects in each and every disc molded using the damaged stampers.
Additionally, it is important to be able to clean the mold members, such as by the removal of any debris, dirt, dust, lint, fingerprints, and any other foreign materials from the surfaces of the molds, and to maintain the molds in a clean condition and free of such foreign matter, which could cause damage to the stampers and defects in the discs molded therefrom. Therefore, it would be desirable to develop a method for preparing the molds for use in the molding process and apparatus and for maintaining all foreign matter out of the stamper/mold interface.